Some vehicles now contain a display in the dashboard to show the instrument cluster rather than more commonplace mechanical dials. One factor that has limited the widespread acceptance of such displays is the realism with which they can represent the instruments. The current invention attempts to address this issue by describing a display that can produce multiple images at different depths using only a single display as an image source. Such a display could show the instrument panel at one depth and the needles and warning indicators floating above it. This would increase both the visibility and realism of the instruments leading to a wider user acceptance.
A display that can produce multiple images at different depths would have many further applications. For instance it could be used for a car navigation display, to allow way-points or items of interest to float above a background map. It could be used as a personal computer display to add functionality to current operating systems and applications. It could be integrated into a games system to provide limited depth plane 3D. It could be integrated into medical imaging systems to allow the operator to overlay various data sets. In fact many of the applications of current auto-stereoscopic displays would be appropriate for this invention.
The prior art teaches us how to make stereoscopic and auto-stereoscopic displays from a single panel, however, these devices produce a stereo image pair rather than true depth. Drawbacks of auto-stereoscopic displays include: limited head freedom, and eye strain due to conflicting depth cues (convergence—accommodation).
U.S. Pat. No. 4,736,214 (Rogers, filed 16 Jul. 1985), illustrated in FIG. 1, describes a film projector 2 which uses film 4 that contains two images for each time frame, a background image 6 and a foreground image 8. The two images are projected via different length optical paths to produce a motion picture with two depth planes. This generates the multiple depth effect but requires large, expensive film apparatus and a bulky series of mirrors 10, 12, 14 to create the path difference.
Various types of volumetric and multi-panel/multi-screen displays have also been described. Deep Video Imaging (WO99/42889, WO03/040820A1, WO2004/001488A1, WO2004/002143A1 and WO2004/008226A1) describe a display, illustrated in FIG. 2, constructed from two spatial light modulators (SLMs) 16 and 18 overlaid in front of a light source 20 to create a single device with two depth planes. This achieves a similar effect to the current invention but with the following drawbacks. Moiré fringes occur due to the same regular pattern of the black mask on both of the panels 16 and 18. The use of multiple panels 16 and 18 leads to a very low light transmission and thus a very bright backlight is needed. The system is subtractive, so a back pixel must be on for a pixel in front to be seen, which means a light object cannot be shown on a dark background. As light must pass through both layers, parallax effects will occur at boundaries. The display uses multiple SLMs which makes the system expensive compared to a standard display. To increase the number of depth planes the number of SLMs must be increased (there is a 1 to 1 correlation between depth planes and SLMs). The system requires synchronised control of multiple display panels.
Application U.S. Pat. No. 2004/0029636A1 describes a similar multiple panel display device, however, it is specifically targeted at a wagering gaming device.
EP1059626A1 and EP0454423A1 describe multilayer displays but with fixed electrode patterns specifically targeted at certain applications such as a watch and hand-held game. EP1265097A2 refers to a display for an automotive instrument cluster consisting of a matrix addressable display overlaid with a patterned display capable of showing specific vehicle functions. Drawbacks are the same as above for multiple panel displays, but in addition they can only show limited images as dictated by electrode patterns.
EP1093008A1, JP02-262119A, WO91/12554A1, JP62-235929A and U.S. Pat. No. 2002/0105516A1 disclose volumetric displays based on multiple layer scattering and polariser free display panels. These are designed to improve the brightness of the resulting image compared to absorbing display panels, but have a number of drawbacks. The dark (no light) state is produced by the no scattering state. In this case the light is transmitted to the environment which would not be suitable for an automotive display, particularly for night time driving. In addition multiple displays make the system expensive. These types of display also have slow switching times and are not suitable for the wide temperature ranges of the automotive environment.
U.S. Pat. No. 4,333,715, U.S. Pat. No. 2002/0163482A1 (scattering) and U.S. Pat. No. 4,670,744 (reflection) disclose time sequential projection volumetric displays, illustrated in FIG. 3. These operate using a projector 22 to display the images for each plane sequentially in a single display frame. The reflective or scattering panels 24 are then switched on in synchronisation with the images. There are a number of disadvantages. Time sequential projection requires the device to operate faster than video rate, which is difficult with current technologies over a wide temperature range. Also, synchronisation with shutters is required, and the system is bulky due to projection optics.
DaimlerChrysler F500 Mind Car research vehicle shown at the 2003 Tokyo motor show (and described at http://www.daimlerchrysler.com/dccom/0-5-7154-1-150005-1-0-0-149730-0-0-8-7145-0-0-0-0-0-0-0.html) demonstrated an instrument cluster which overlaid, by means of a half-silvered mirror, a standard cluster and an LCD panel. However, this requires extra volume as two displays must be at an angle to each other, and the multiple displays make the system expensive.
WO98/10584A2, illustrated in FIG. 4, describes a device using multiple display devices 26 and 28 and a partially silvered mirror 30 to produce two image planes at different depths. This embodiment is bulky and costly due to using two displays. In a separate embodiment, the device produces two images derived from large regions of the same display device, as illustrated in FIG. 5. FIG. 5 shows a display device 32 divided into foreground elements 34 and background elements 36. Light from the foreground elements 34 passes directly to expansion elements 38, whereas light from the background elements 36 is reflected first by mirrors 40 and then by partially reflecting mirrors 42 before reaching the expansion elements 38. The background image, formed from the background elements 36, therefore appears to the viewer to be further away than the foreground image which is formed from the foreground elements 34. As the elements 34 and 36 are large, additional elements 38 are required to expand the sections of the image to fill the entire display region. These extra elements 38 lead to a reduced head freedom due to the f-number of the lenses, and the additional elements require exact alignment with the regions of the display. Two mirror elements 40, 42 are required per section which is both bulky and costly. Any aberration in the lenses would cause image distortion as the viewer moves relative to the display even if it is perfectly compensated on axis.
WO98/10584A2 also describes a third configuration, illustrated in FIG. 6, which is a time sequential method in which a rod 44 with mirrors, lenses or projections screens 46, 48 attached is rotated in synchronisation with images displayed by a projector 50. The items attached to the rod 44 are at different distances from the display device so that the observer sees two different depth images. The device requires a bulky projector 50 and spinning rod 44, and rotation of the rod 44 must be synchronised with the projected images.